(2024) Process Safety and Environmental Protection_Environmentally-friendly alkaline ionized water pretreatment and hydrolysis of macroalga via microwave-assisted heating to improve monosaccharide yield for bioethanol production

Chen W.-H.; Liu L.-X.; Khoo K.S.; Sheen H.-K.; Kwon E.E.; Saravanakumar A.; Chang J.-S.

(Institution of Chemical Engineers) Process Safety and Environmental Protection ISSN: 9575820 Vol.189 Issue. Article No. DOI: 10.1016/j.psep.2024.06.095

This study synthesizes three sequential steps: pretreatment, acid hydrolysis, and enzyme hydrolysis for bioethanol and hydrochar production from macroalga Gracilaria. The Taguchi method is employed separately in each step to optimize relevant operating factors, aiming to maximize the monosaccharide yield. During pretreatment, environmentally friendly alkaline ionized water is utilized as it does not contain chemical additives. Afterward, microwave-assisted hydrolysis is adopted to enhance the monosaccharide yield of the macroalga for bioenergy production. The results show that the total sugar of Gracilaria undergoing acid hydrolysis alone is 28.72 g‧L⁻¹. The total sugar content after alkaline pretreatment followed by acid hydrolysis is 32.64 g‧L⁻¹, and it increases to 34.76 g‧L⁻¹ after adding enzymes. Meanwhile, the higher heating value of Gracilaria increases from 10.884 MJ‧kg⁻¹ to 12.620 MJ‧kg⁻¹ after undergoing alkaline pretreatment. After the acid and enzyme hydrolysis processes, it increases to 15.164 MJ‧kg⁻¹. The solid biofuel's calorific value increases by 39 % from the three-stage processes. The liquid product combined with Saccharomyces cerevisiae can produce bioethanol, while the produced hydrochar can be used as a solid fuel. This research promotes the development of macroalgal biomass for energy and environmental applications, thereby advancing the circular bioeconomy. © 2024 The Institution of Chemical Engineers

The authors acknowledge the financial support of the National Science and Technology Council, Taiwan, R.O.C., under contracts NSTC 112-2218-E-006-025- and NSTC 112-2218-E-002-052- for this research, and the use of EM000700 of NSTC 113-2740-M-006-002 belonging to the Core Facility Center of National Cheng Kung University. This research is also partly supported by Higher Education Sprout Project, Ministry of Education to the Headquarters of University Advancement at National Cheng Kung University (NCKU).